The present invention is directed to bicycle hubs used to support wheel rims via spokes.
The wheel on a bicycle usually has a hub shell rotatably supported on an axle, spokes that are engaged in the hub, a rim that is linked to the hub by nipples that thread onto the radially outward ends of the spokes, and a tire that is mounted on the rim. The two ends of the hub shell are each provided with a flange part that is used to engage the spokes. Through holes that are used to engage the spokes are made in these flange parts in the hub axle direction at distance from each other in the circumferential direction. The spoke is usually bent on its distal side, and a distal flange that is formed in the shape of a nail head is disposed at this bent distal end. The distal end is supported in one of the through holes in the hub flange. Male threads are formed on the base side of the spoke for engaging the nipple, and the nipple has a flange that engages with the rim.
With a spoke structured in this manner, the nipple is installed in a nipple hole formed in the rim, the spoke is inserted from its base side into the through hole of the hub, the distal flange is engaged in the through hole, and the male threads on the base side of the spoke are threaded into the female threads of the nipple installed in the rim, thereby linking the hub and the rim.
With this type of wheel, tension is always acting on the spoke shafts intermittently, so fatigue can cause the spoke shafts to break at the bent portion on the base side of the distal flange. In order to prevent this, Japanese Utility Model Publication H2-22321 discloses a wheel hub that allows the mounting of straight spokes in which the base side of the distal flange of the spoke is roughly linear. This hub has a plurality of spoke attachment parts at a distance from each other in the circumferential direction on both ends of the hub shell. In the spoke attachment parts are made a pair of spoke holes that go through in the circumferential direction (the tangential direction) at the same radial twisting position and that are aligned in the axial direction. These spoke holes are made at a slight angle with respect to the circumferential direction, and are formed such that the spoke shafts face slightly inward. With a wheel in which this hub is used, the spokes are connected to the rim by being bent slightly outward at the place where they come out of the spoke holes.
Since this type of hub allows straight spokes to be mounted, there is less spoke breakage than with a wheel in which spokes having bent distal portions are mounted. However, since the spoke holes are arranged so that they are aligned in the axial direction, the spacing in the hub axial direction of the left and right spokes that are engaged in the spoke holes on the inside in the axial direction is narrower than that on a wheel in which spokes having bent distal portions are mounted, which is a problem in that the horizontal rigidity of the wheel (the rigidity in the hub axial direction) is lower.